The Great Barrier Reef in Peril: Climate Change, Resilience, and the Fight for Survival

The Great Barrier Reef is the world’s largest living reef, stretching for 1,300 miles (2,300 kilometers) located off the coast of Queensland in Australia. In 1975 the Australian government created the Great Barrier Reef Marine Park, which covers over 130,000 m² (345,000 km²). Since 1981, the Great Barrier Reef has been listed as a World Heritage Site.

During May 1998, marine scientists argued that the Great Barrier Reef had experienced its worst case of coral bleaching in recorded history. A mere eighteen years later, during another strong El Nino event, 99 percent of northern reefs sustained significant bleaching. Corals can adapt to a certain amount of gradual warming that precedes bleaching. However, a report in Science published in 2016 found that massive, sudden warming of their aquatic habitat overwhelms these defenses, killing corals on a massive scale. During the 2015-16 El Nino, more than half of the corals in the Great Barrier Reef’s northernmost 700 miles died, but 95 percent of those farther south survived, according to Australia’s ARC Center of Excellence for Coral Reef Studies.

Tracy D. Ainsworth and colleagues, having studied Australia’s Great Barrier Reef, found that the 2015-16 El Nino, which produced record high temperatures in the oceans as well as the atmosphere, disabled corals’ natural bleaching mechanisms. Furthermore, they wrote: “Near-future increases in local temperature of as little as 0.5°C result in this protective mechanism being lost, which may increase the rate of degradation of the GBR.”

Eight of the ten reefs that Roberts and colleagues would like to protect are already being dramatically altered by human activity through fishing, logging, and farming. The felling of forests, for example, means that soils are easily eroded, often depositing mud that can choke reefs. Farming releases nutrients that encourage seaweeds to grow where corals once flourished. “One of the arguments is that there is nothing we can do, it is all going to go to hell, and that coral reefs are doomed. The other argument is that we should work very hard to try and do something about protecting them,” Roberts said. “The question then is how? Where are we going to focus our efforts, given that we don’t have the resources to do all that we would like? We cannot save all coral reefs everywhere” (Radford 2002, 12).

Not only can some corals adapt to warmer water, but they may be able to pass this tolerance on to succeeding generations. According to a report in Nature, Researchers have suggested that corals physiologically acclimatize to higher temperatures rather than inherit heat tolerance. To test this idea, Line Bay at the Australian Institute of Marine Science in Townsville, Australia and Mikhail Matz at the University of Texas at Austin and their teams bred corals (Acropora millepora) from two locations in Australia separated by 5 degrees of latitude. Offspring produced by parents from the warmer area had an up to 10 times greater chance of survival. (Corals Inherit, 2015)

Some varieties of coral (notably Porites cylindrica, in Australia’s Heron Island Lagoon and the Great Barrier Reef) resist ocean acidification, according to a study published in 2015 in the Proceedings of the National Academy of Sciences by researchers at the University of Queensland and the University of Western Australia. This type of coral contains a calcifying fluid at a constant pH level, even as the acid level changes in the water around it. “The regulatory mechanism allows the coral to grow at a relatively constant rate, suggesting it may be more resilient to the effects of ocean acidification than previously thought,” said lead author Lucy Georgiou, of UWA’s ARC Centre of Excellence for Coral Reef Studies.

Scientists investigated 328 colonies of massive Porites corals on the Great Barrier Reef off Australia that grow to more than 6 meters tall over decades to centuries. Results from sixty-nine sections of the reef found that calcification had declined 14.2 percent between 1990 and 2005, impeding the reefs’ growth by 13.3 percent. Such a sudden, massive decline in the reef’s calcification had no precedent in recorded history—about 400 years. Increasing temperature stress and a rising carbon dioxide level in the water around the reef are the probable causes. “This study has provided the first really vigorous snapshot of how calcification might be changing [worldwide],” said marine biologist Ove Hoegh-Guldberg of Australia’s University of Queensland. “The results are extremely worrying” (Pennisi 2009: 27).

Terry Hughes at James Cook University in Townsville, Australia, and colleagues hold out some hope that although climate change will alter the species composition of many coral reefs, it will not completely wipe them out. Hughes and his team collected samples at 132 sites in Australia’s Great Barrier Reef. “Of the twelve coral taxa sampled,” they reported, “eleven showed significant differences in abundance across the reef, regardless of how susceptible they were to thermal stress and bleaching. These differences in abundance did not follow changes in latitude or temperature. This flexibility may enable coral reefs to continue functioning as the environment alters with climate change” (Can Coral Cope 2012).

To answer the Great Barrier Reef challenges, local Queensland and the Australian government developed the Reef 2050 plan in 2015. The plan partially reacted to UNESCO’s consideration of placing the reef on its list of endangered heritage sites. The plan received much acclaim for its attempt to include the Australian Aborigines in the document’s implementation, to reduce the prevalent crown-of-thorns starfish population that periodically threatens to devour a large part of the reef, and to decrease pollution through runoff into the area. Critics of Reef 2050 point out, however, that while the plan includes critical local measures to ensure the reef’s future well-being, it did little to address the real threat to the site: global climate change. The Australian government, they continued, had committed to a 2030 emission reduction. Still, the less than 30 percent reduction would not have the expected result to keep the earth’s temperature from rising. It would continue to expose the reef to warming water temperatures and ocean acidification. Bruce E. Johansen

FURTHER READING:Ainsworth, Tracy D., Scott F. Heron, Juan Carlos Ortiz, Peter J. Mumby, Alana Grech, Daisie Ogawa, C. Mark Eakin, and William Leggat. 2016. “Climate Change Disables Coral Bleaching Protection on the Great Barrier Reef.” Science 532: 338-42.

“Can Coral Cope with Climate Change?” 2012. Nature 484: 290.
“Corals Inherit Love for Heat.” 2015. Nature 523: 8.

Georgiou, Lucy, James Faltera, Julie Trottera, David I. Kline, Michael Holcomb, Sophie G. Dove, . . . Malcolm McCulloch. 2015. “PH Homeostasis during Coral Calcification in a Free Ocean CO₂ Enrichment (FOCE) Experiment, Heron Island Reef Flat, Great Barrier Reef.” Proceedings of the National Academy of Sciences, October 6. http://www.pnas.org/content/early/2015/10/01 /1505586112.full.pdf?sid=26b9f3e1-4ff7-4247-821f-e806352a8708. Accessed November 12, 2016.

Innis, Michelle. 2016. “Climate-Related Death of Coral Around World Alarms Scientists.” The New York Times, April 9. http://www.nytimes.com/2016/04/10/world/asia/climate-related-death -of-coral-around-world-alarms-scientists.html. Accessed November 12, 2016.

Kolbert, Elizabeth. 2016. “Unnatural Selection: What will it take to Save the World’s Reefs and Forests?” The New Yorker, April 18, pp. 22-8.

NASA Earth Observatory. 2009. “Scientists Find Heat-Tolerant Coral Reefs that May Resist Climate Change.” http://earthobservatory.nasa.gov/Newsroom/view.php?id = 38819&src = eoa -manews. Accessed November 12, 2016.

Pennisi, Elizabeth. 2009. “Calcification Rates Drop in Australian Reefs.” Science 323: 27.

Radford, Tim. 2002. “Ten Key Coral Reefs Shelter Much of Sea Life: American Association Scientists Identify Vulnerable Marine ‘Hot Spots’ with the Richest Biodiversity on Earth.” London Guardian, February 15, p. 12.

University of Western Australia. 2015. “Self-Regulating Coral Protect Themselves Against Ocean Acidification.” University News, October 6. http://www.news.uwa.edu.au/201510068035 /research/self-regulating-coral-protect-themselves-against-ocean-acidification. Accessed November 12, 2016.